1. Field of the Invention
This invention relates to an ophthalmic measuring apparatus capable of measuring the refractive power of an eye and the shape of cornea at a time.
2. Description of the Prior Art
Generally, when examination of eye refraction is to be carried out, measurement of the shape of the cornea is also carried out for the purpose of the examination of the presence of astigmatism and of the examination of the axis of astigmatism and the degree of astigmatism. Particularly, with the recent spread of contact lenses, examination of the shape of cornea has become more important to choose the base curve thereof.
Heretofore, when such an examination is to be carried out, it has been usual to accomplish "contact lens prescription" by first measuring the shape of the cornea of the examinee by an instrument called an ophthalmometer or a keratometer, choosing the base curve and determining the degree of corneal astigmatism, thereafter screening the full refractive power and the full astigmatism by an unconscious (objective) refraction examination using a refractometer or the like, and effecting a self-conscious (subjective) refraction examination and final determination of the base curve by the trial lens method. Measurement of the shape of cornea has been proposed by U.S. patent application Ser. No. 416,355, and Japanese Laid-open Patent Application No. 161031/1981, etc. are known for the measurement of eye refractive power.
As described above, heretofore, measurement of the shape of cornea and measurement of refractive power have been carried out discretely by the use of different instruments and thus, the time and labor required for the measurements have been a considerable burden to both of the examiner and the examinee.
Presently, when overall eye refractive power is to be measured, the eye to be examined is caused to watch a fixation chart provided in the apparatus and the eye to be examined is fixed, and then a predetermined visual target is projected onto the fundus of the eye to be examined and the reflected image thereof is received by a detector, and they are analyzed to thereby obtain a measured value.
There are two kinds of fixation charts for measurement of eye refractive power, namely, a slide photograph of landscape or the like and a radial pattern. The latter radial pattern is such that the center thereof is watched. Now, when the shape of cornea is to be measured, the result of the measurement is affected more by the movement of the examinee than in the case of the measurement of eye refractive power. Therefore, it is necessary to provide a fixation chart for measurement of the shape of cornea, to cause the eye to be examined to watch the fixation chart more concentratedly and to thereby positively fix the eye to be examined.
Where a slide of landscape or the like is used as a common fixation chart for measurement of eye refractive power and for measurement of the shape of cornea, the examinee may be puzzled which portion of the slide to watch and therefore, a slide of landscape or the like is unsuitable as a fixation chart for measurement of the shape of cornea. So, there is considered a case where a radial pattern is used as a common fixation chart. However if the pattern is fixed at the orthoptic position, the pattern will be blurred and cannot be viewed in the case of an examinee of a medium or strong degree of short-sightedness or long-sightedness. Accordingly, it is difficult to fix the eye for examination.